# Unseen Passage

For Class 4 to Class 12

# Electricity Class 10 Science Important Questions

Please refer to Electricity Class 10 Science Important Questions with answers below. These solved questions for Chapter 12 Electricity in NCERT Book for Class 10 Science have been prepared based on the latest syllabus and examination guidelines issued by CBSE, NCERT, and KVS. Students should learn these solved problems properly as these will help them to get better marks in your class tests and examinations. You will also be able to understand how to write answers properly. Revise these questions and answers regularly. We have provided Notes for Class 10 Science for all chapters in your textbooks.

## Important Questions Class 10 Science Chapter 12 Electricity

All Electricity Class 10 Science Important Questions provided below have been prepared by expert teachers of Standard 10 Science. Please learn them and let us know if you have any questions.

ONE MARK QUESTIONS

Question: State a difference between the wire used in the element of an electric heater and in a fuse wire.
Answer: The wire used in element of electric heater has high resistance and high melting point where as a fuse wire has a low resistance and low melting point.

Question: Give an example of a metal which is the best conductor of heat.
Answer: Gold, Silver, Copper etc. metals are good conductor of heat.

Question: What is the lowest resistance that can be obtained by combining four coils of resistances 4 W , 8 W , 12 W and 24 W ?
Answer: If the resistances are combined in parallel then we shall get the lowest resistance. In parallel combination:

1/R=1/R1+1/R2+1/R3+1/R4

=1/4+1/8+1/12+1/24

=6+3+2+1/24=12/24=1/2
R=2Ω

Question: Define resistivity of a material.

Resistivity, P=R A/l
if
A = 1, l = 1 then r = R i.e. resistivity of a material is the resistance of a conductor of this material whose length and area of cross- section both are unity.
or
Resistivity of a material is the resistance of a conductor of this material whose volume is unity.
Question: State Ohm’s law.
Answer: If the physical conditions of a conductor remain same then current through a conductor is irectly proportional to the potential difference b/w the two ends of the conductor.
I ∝  V ⇒ V = IR

Question: (a) Name the instrument/device used to measure electric current in a circuit.
(b) How is an ammeter connected in a circuit to measure current flowing through it?
Answer: a. Ammeter is used to measure electric current.
b. Ammeter is connected in series in an electric circuit.

Question: When is potential difference between two points said to be 1 volt?
Answer: Potential difference betweeen two point is said to be 1 Volt if the amount of work done in bringing 1 C
charge between them is 1 J.

Question: How does the resistivity of alloys compare with those of pure metals from which they may have been formed?
Answer: The resistivity of pure metals is lesser than resistivity of alloys with which these alloys are made.

TWO MARKS QUESTIONS

Question:  Elements of electric toasters and electric iron are made of an alloy rather than a pure metal. Give two reasons to justify the statement.
Answer: a. Alloys have higher resistivity than their constituents pure metals.
b. At high temperature alloys do not oxidise.

Question:  What is the resistance of an ideal voltmeter?
Answer: The resistance of an ideal voltmeter is infinite.

Question:  Mention two special features of the material to be used as element of an electric iron.
Answer: A material to be used as element of an electric iron
must have (i) high melting point, (ii) high resistivity.

Question:  A large number of free electrons are present in metals yet no current flows in the absence of electric potential across it. Explain the statement with reason.
Answer: Though there are large number of free electron present in a conductor, but their motion is random motion in the absence of potential difference. Their average velocity is zero. Hence there is no current flowing in conductor. But when a potential difference is applied across the ends of the conductor, it sets the electrons to move in a direction. The motion of charge produces an electric current in the conductor.

Question:  Give reason for the following:a. Tungsten used almost exclusively for filament of electric lamp.
b. Why do we use copper and aluminium wires for transmission of electric current?
Answer: a. Tungsten is used in making the filament of electric lamp because it has high resistivity and high melting point.
b. The copper and aluminium have low resistivity and high conductivity.
Question:  (a) What are the values of mA and m A?
(b) Draw the symbols of battery and rheostat.
1 mA = 1 milli ampere = 10-3 A
1 μ A = 1 micro ampere = 10-6 A 33

THREE MARKS QUESTIONS

Question:  (a) How is the direction of electric current related to the direction of flow of electrons in a wire?
(b) Calculate the current in a circuit, if 500 C of charge passes through it in 10 minutes.
Answer: a. The direction of flow of electrons is opposite to the direction of conventional current.
b. Q = 500 C, t = 10 mts = 10X60 = 600 s
I=Q/ t=500/600A
I = 0.83 A

Question: (a) Explain why a conductor offers resistance to the flow of current.
(b) Differentiate between conductor, resistor and resistance.
Answer: a. When a current is passed through a conductor, the atoms or molecule of the conductor produce an hindrance in the path of flow of electron. This hindrance in the path of flow of charge is called resistance of the conductor.
b. A substance which allow to pass the charges through them easily is called a conductor.
Resistor : A conductor having some value of resistance is called a resistor.
Resistance : It is the property of any conductor by virtue of which it opposes the flow of charge through it.

Question: (a) List the factors on which the resistance of a conductor in the shape of a wire depends.
(b) Why are metals good conductors of electricity whereas glass is a bad conductor of electricity?
Give reason.
(c) Why are alloys commonly used in electrical heating devices? Give reason.
Answer: a. Factors on which resistance of a wire depends:
i. Resistance is directly proportional to length.
ii. Resistance is inversely proportional to area of cross-section.
R ∝ l , R∝ 1/A
R ∝ A 1/A or R=P l/A
b. Metal are good conductor due to having large number of free electrons and their low resistivity.
Glass is a bad conductor because it has no free electrons and its resistivity is higher.
c. Alloys are commonly used in electrical heating devices due to their high resistivity and high melting point which produces more heat.

Question: Name and define SI unit of resistance. Calculate the resistance of a resistor if the current flowing through it is 200 m A, when the applied potential difference is 0.8 V.
Answer: a. SI unit of resistance is ohm (Ω) 1 Ω=1 V/1 A
b. The resistance of a conductor is said to be 1 ohm if a current of one amp flows through it when a potential differences of 1 volt is applied across it.
c. R=V/I=0.8/200 X 10-3=4Ω

Question: Resistivity of two elements A and B are = 1.62X 10-8 Ω m and 520X10-8 Ω m respectively.
Out of these two, name the element that can be used to make:
a. filament of electric bulb.
b. wires for electrical transmission lines. Justify your answer in each case.
Given:       PA = 1.62X10-8 Ω m
PB = 520X10-8 Ωm

a. For filament of electric bulb resistivity must be higher i.e. 520X10-8 Wm . So element B is used for filament.
b. For electric transmission resistivity must be lower which is of element A.

FIVE MARKS QUESTIONS

Question: (a) Why is the series arrangement not used for domestic circuits?
(b) Why is the tungsten used almost exclusively for filament of electric lamps?
(c) Why are the conductors of electric heating devices such as bread toasters and electric irons made of an alloy rather than a pure metal?
(d) Why are copper and aluminium wires usually employed for electricity transmission?
(e) Why does the cord of an electric heater not glow while the heating element does?
Answer: a. In the series arrangement if any device fails to work, circuit will be broken and other devices stop working. In series combination current remains same. Where as different devices requires different current.
b. Tungsten is used due to its high resistivity and high melting point.
c. Alloys have higher resistivity than their pure constituent and hence produces more heat.
d. Copper and aluminium are good conductors and have low values of resistivity so these are used for electric transmission.
e. Cords core made up of good conductor with low resistivity where as heating elements are made up of alloys of higher resistivity to produce more heat.

Question: Define power. State the difference between 1 watt and 1 watt hour. Establish the relationship between unit of electric energy and SI unit of energy. An electric heater rated 1000 W/220 V operates 2 hours daily.
Calculate the cost of energy to operate for 30 days at the rate of Rs 5.00 per kWh.
Answer: Electric Power: P is defined as the rate at which electric energy is consumed in an electric circuit.
1 watt is the power consumed by an electric appliance that carries 1A current when a potential difference of 1 volt is applied across it. Whereas 1 Wh. is the unit of electric energy, which is consumed by an electric appliance of 1 W power in one hour.
Commercial unit of electric energy is kWh.
1 kWh = 1000WX60X60 s
1 kWh = 3.6X106 J
Energy consumed by heater in one month
= 1000WX2hX30 days = 60 kWh = 60 units
Total cost @Rs.5/-kWh = 5X60 = Rs.300
Question: What do you mean by heating effect of electric current? Explain the production of heat in a resistor by flow of electric current through it. Name two devices based on heating effect of current.
Answer: When current is passed through a conductor, heat is produced. Production of heat in a conductor on passing the current is called heating effect of current.
When a current is passed in a conductor by applying a potential difference, electrons get accelerated and collide with the atoms of the conductor. During the collision there is a loss of kinetic energy. This loss in K.E. appears in the form of heat energy in the conductor 1. Electric heater, 2. Bulb.

Question: What is meant by resistance of a conductor? Name and define its SI unit. List the factors on which the resistance of a conductor depends. How is the resistance of a wire affected if:
a. its length is doubled,
Answer: Property of any conductor by virtue of which it opposes the flow of current in the conductor is called its resistance.
SI unit of resistance is Ohm. If by applying a potential difference of 1 volt the current in the conductor is 1 A. Then the resistance of the conductor is said to be 1 ohm.
Factor affecting resistances:
a. If length is double then resistance also becomes doubled.
b. If radius is doubled then area A = π(2r)2 becomes 4 times, then the resistance becomes 1/4.
Question: Two electric lamps of 100 W and 25 W respectively are joined in parallel to a supply of 200 V. Calculate the total current flowing through the circuit.
Bulbs 100 W 25 W
V = 200 V 200 V
Total P = P1+ P2
= 100 + 25 = 125W
I =P/V=125/200A
I = 0.625 A

Question: Calculate the resistance of an electric bulb which allows a 10 A current when connected to a 220 V power source.
I = 10 A
V = 220 Volt.
Resistance of bulb =V/I=220/10=22Ω

Question: The rating of an electric heater is 1100 W, 220 V. Calculate its resistance when it operates at 220 V. Also, calculate the energy consumed in kWh in the month of November, if the heater is used daily for four hours at the rated voltage.
P = 1100W
V = 220 V
R=V2/P=220X220/1100Ω=484/11Ω=484/11Ω=44Ω

Total energy consumed in the month of Nov. (i.e. 30days) @ 4 hr per day.
E = PX t
= 1100X4XhrX30
= 1100X120Wh
E = 132 kWh

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